Question

Titration ( Standardization of Sodium Carbonate with 0.01 M H2SO4) : Back calculating the original concentration of H2SO4, PLEASE HELP!

Rxn : H2SO4 and Na2CO3 >>> Na2So4 +H20 + CO2

We want 0.01 M H2SO4 . By using 18 M H2SO4 and final volume of 1000 ml . Using a micropipette we transferred 0.56 ml (555 uL) of 18 M H2SO4 and diluted up to 1000 ml with freshly boiled distilled water (To release CO2) . We then filled the burette with the 0.01 M H2SO4 that we prepared. In an Erlen Meyer flask we measured dried sodium carbonate (0.1150 g) and put some distilled water in there (we didn't measure the water) Should we? added phenalthalien in the flask with sodium carbonate and titrated it with the H2SO4 in the burette. It took 52.88 ml to titrate. When I back calculated to make sure we made the correct Molarity of H2So4 (0.01) I get 0.02 M H2SO4.

My calculation : 0.1150 g na2co3 / 105.98 g Na2Co3 / 0.0528 L = 0.02 M .

PLEASE LET ME KNOW IF IM DOING THE PROCEDURE OR CALCULATION WRONG! THANKS!!

Answer 1

For making 1000 ml of 0.01M H₂SO₄ from 18M H₂SO₄ we should do

M₁V₁ = M₂V₂

18* V₁ = 0.01*1000

V₁= 0.555 ml

i.e, if you add 0.56 ml of 18 M H₂SO₄ in 1000 ml of water then molarity of solution is 0.01 M

Up to here it is correct, then to cross check the molarity of H₂SO₄ by titration we should known the molarity of Na₂CO₃

For example if you dissolve 0.115 g of Na₂CO₃ in 100 ml of water then molarity of Na₂CO3 is 0.01 M as shown below

M = (wt/mol.wt)*(1000/V (ml))

M of Na₂CO3 = (0.115/106)*(1000/100) = 0.01 M

Now you take100 ml of 0.01 M Na₂CO₃ in Erlen Meyer flask, add phenalthalien 2-3 drops then titrate with 0.01 M H₂SO₄ then

M₁V₁ (H₂SO4) = M₂V₂ (Na₂CO₃)

0.01*V1 = 0.01*100

V1=0.01*100/0.01 = 100 ml

Then your burette reading should be 100 ml which indicates that the molarity of H₂SO4 is 0.01 M

So you should known the volume of water used for making Na₂CO₃ solution from which you can known the molarity of Na₂CO₃ solution, inturn from which you can check the molarity of H₂SO4 solution used for titration